Isn't this / ?
Why is there a constant for it? It's not like it can change, right?
PATH_SEPARATOR is the character used to separate many paths in a unique string (like include_path in php.ini).
Its value is ':' on a UNIX system and ';' on a Windows system.
What you're talking about ('/' on UNIX and '\' on Windows) is the DIRECTORY_SEPARATOR constant.
As your original question states: "Why is there a PATH_SEPARATOR constant?", windows uses a semi-colon ;, while other systems use a colon :
However I think you've mistaken PATH_SEPARATOR with DIRECTORY_SEPARATOR
PATH_SEPARATOR delimits multiple paths in the same string. For example when used in windows environment variables.
c:\path\to\a;c:\path\to\b
DIRECTORY_SEPARATOR separates the directories within the path: In Windows
\
In other systems
/
As mentioned by others, windows also accepts /
It can. It is \ in Windows and / in Linux (and prettymuch everywhere else), although modern versions of Windows do accept / as a separator.
Ooops this is about the DIRECTORY_SEPARATOR constant.
PATH_SEPARATOR is indeed the constant to separate various paths as seen in PéCés answer.